U.S. patent number 7,399,339 [Application Number 11/153,844] was granted by the patent office on 2008-07-15 for polyoxometalate material for gaseous stream purification at high temperature.
This patent grant is currently assigned to Gas Technology Institute. Invention is credited to Qinbai Fan, William E. Liss, Michael Onischak.
United States Patent |
7,399,339 |
Fan , et al. |
July 15, 2008 |
Polyoxometalate material for gaseous stream purification at high
temperature
Abstract
A method for purification of a gaseous stream having at least
one impurity in which a porous material having at least one
polyoxometalate-based material is contacted with the gaseous stream
and the at least one impurity is passed through the porous
material, producing a purified gaseous stream.
Inventors: |
Fan; Qinbai (Chicago, IL),
Onischak; Michael (St. Charles, IL), Liss; William E.
(Libertyville, IL) |
Assignee: |
Gas Technology Institute (Des
Plaines, IL)
|
Family
ID: |
37572074 |
Appl.
No.: |
11/153,844 |
Filed: |
June 15, 2005 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20060283323 A1 |
Dec 21, 2006 |
|
Current U.S.
Class: |
95/55; 95/45;
96/10; 96/4 |
Current CPC
Class: |
B01D
53/228 (20130101); B01D 67/0041 (20130101); B01D
67/0079 (20130101); B01D 69/141 (20130101); B01D
71/024 (20130101); C01B 3/503 (20130101); B01D
53/229 (20130101); C01B 2203/0495 (20130101); B01D
67/0011 (20130101); B01D 71/00 (20130101); B01D
71/52 (20130101); B01D 71/60 (20130101); B01D
71/62 (20130101); B01D 71/68 (20130101); B01D
2325/22 (20130101); B01D 2325/24 (20130101); C01B
2203/0405 (20130101); C01B 2203/0465 (20130101); C01B
2203/047 (20130101); C01B 2203/0475 (20130101); C01B
2203/0485 (20130101) |
Current International
Class: |
B01D
53/22 (20060101); B01D 71/00 (20060101) |
Field of
Search: |
;95/45,47-54,55
;96/12-14,10 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Duane
Assistant Examiner: Clemente; Robert A
Attorney, Agent or Firm: Fejer; Mark E.
Claims
We claim:
1. A method for hydrogen purification comprising the steps of:
contacting a porous material comprising at least one
polyoxometalate with a fluid stream comprising hydrogen gas and at
least one impurity; and passing said at least one impurity through
said porous material, producing purified hydrogen.
2. A method in accordance with claim 1, wherein said porous
material is a ceramic.
3. A method in accordance with claim 2, wherein said
polyoxometalate is dispersed throughout said ceramic.
4. A method in accordance with claim 2, wherein said
polyoxometalate is disposed on a surface of said ceramic.
5. A method in accordance with claim 1, wherein said porous
material is in a form of a ceramic tube and said fluid stream is
passed through said ceramic tube.
6. A method in accordance with claim 1, wherein said fluid stream
is a hydrogen-containing reformate fuel.
7. A method in accordance with claim 1, wherein said at least one
impurity is a polar molecule.
8. A method in accordance with claim 1, wherein said at least one
impurity is selected from the group consisting of H.sub.2S, HCl,
NH.sub.3, CO.sub.2, water and mixtures thereof.
9. A method in accordance with claim 1, wherein Said
polyoxometalate is a polymer having the structure ##STR00004##
10. A method in accordance with claim 1, wherein said
polyoxometalate is a polymer having the structure ##STR00005##
11. A method in accordance with claim 1, wherein said
polyoxometalate is a polymer having the structure ##STR00006##
12. A method for removal of at least one impurity from a gaseous
stream comprising said at least one impurity, the method comprising
the steps of: contacting a porous ceramic material comprising at
least one polyoxometalate with the gaseous stream; and passing said
at least one impurity through said porous material, producing at
least a partially purified gaseous stream.
13. A method in accordance with claim 12, wherein said
polyoxometalate is dispersed throughout said ceramic.
14. A method in accordance with claim 12, wherein said
polyoxometalate is disposed on an outer surface of said
ceramic.
15. A method in accordance with claim 12, wherein said porous
material is in a form of a ceramic tube and said gaseous stream is
passed through said ceramic tube.
16. A method in accordance with claim 12, wherein said gaseous
stream comprises a hydrogen-containing reformate fuel.
17. A method in accordance with claim 12, wherein said at least one
impurity is a polar molecule.
18. A method in accordance with claim 12, wherein said gaseous
stream comprises flue gases.
19. A method in accordance with claim 12, wherein said
polyoxometalate is a polymer having the structure ##STR00007##
20. A method in accordance with claim 12, wherein said
polyoxometalate is a polymer having the structure ##STR00008##
21. A method in accordance with claim 12, wherein said
polyoxometalate is a polymer having the structure ##STR00009##
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for removal at
high temperatures of undesirable components, or impurities, from a
gaseous stream containing said undesirable components. Depending
upon the source of the gaseous stream, e.g. fossil fuel combustion
or reforming, the undesirable components that may be addressed by
various embodiments of the method and apparatus of this invention
include, but are not limited to, NO.sub.x, SO.sub.x, HgO, H.sub.2S,
CO.sub.2, HCl, and NH.sub.3. More particularly, this invention
relates to the use of polyoxometalate materials for purification of
gaseous streams, such as hydrogen-containing gaseous streams
produced by fossil fuel reforming, flue gases produced by fossil
fuel combustion, and solid fuel gasification products, and for
processing gaseous streams such as natural gas processing,
comprising these undesirable components at high temperatures. The
polyoxometalate materials selectively remove the undesirable
components by absorption and/or diffusion through a layer of the
polyoxometalate materials by concentration difference and
concentrate them for more effective and efficient removal by
currently available technologies.
2. Description of Related Art
H.sub.2S, CO.sub.2, HCl, and NH.sub.3 are byproducts from natural
gas, coal gasification or fossil oil reforming which can produce a
hydrogen-rich fuel. Removing these contaminants from the
hydrogen-rich fuel supplied to proton exchange membrane fuel cell
systems (PEMFC) is necessary as the H.sub.2S, HCl, and NH.sub.3
poison the fuel cell membrane and catalysts. The CO.sub.2 and extra
water then dilute the fuel and reduce the fuel cell performance.
However, these can be removed by other means.
Current techniques for removing these contaminants include
low-temperature membrane gas separation to remove CO.sub.2 and
NH.sub.3 at temperatures less than about 120.degree. C., CuO/ZnO
catalysts to remove H.sub.2S at moderately high temperatures, and
Pd-based membranes for hydrogen separation. However, these
techniques generally suffer from various limitations including
short lifetimes and non-continuous removal of impurities, and they
require substantial efforts for regeneration.
Polyoxometalate-based organic-inorganic hybrid materials, which are
well-defined, discrete transition metal oxide clusters with a
variety of organic ligands as charge-compensating cations, have
been applied in many fields, such as catalysis, medicine,
materials, surface chemistry, and photo- and electro-chromism.
These unique materials are thermally stable at temperatures greater
than 300.degree. C. and capable of reversible sorption of gases and
organic vapors (CO.sub.2, CHCl.sub.3, etc.). In addition,
polyoxometalates are based on very low-cost starting materials,
thereby providing the potential for very attractive manufacturing
costs.
Pressure swing adsorption (PSA) is an adiabatic process for
purification of gases in which the impurities in the gases are
removed by adsorption through suitable adsorbents in fixed beds
contained in pressure vessels under high pressure. Regeneration of
the adsorbents is accomplished by countercurrent depressurization
and by purging at low pressure with previously recovered
substantially product-quality gas. To obtain a continuous flow of
product, a minimum of two adsorbers is required. In this manner,
one adsorber receives feed gas and actually produces a product gas
of desired purity while the other adsorber performs the steps of
depressurization, purging and repressurization back to the
adsorption pressure. After such adsorbent regeneration and
repressurization, the functions of the adsorbers are switched.
Depending upon the type of impurity to be adsorbed and removed,
adsorbents to be used comprise zeolitic molecular sieves, activated
carbon, silica gel and activated alumina. Typically, layers of
different adsorbent beds are used, thereby dividing the adsorber
contents into a number of distinct zones. Monitoring and proper
control of process parameters ensures a stable operation. Stable
operation means a pendulating swing in each particular location, in
adsorber bed or piping, of values for all parameters, i.e.
pressure, temperature, flow and composition of gaseous and adsorbed
phase.
SUMMARY OF THE INVENTION
The invention claimed herein is a method for selectively separating
impurities in a gaseous stream from the gaseous stream employing a
material specifically tailored for the separation, producing a
significantly purified gaseous stream. In accordance with one
embodiment of this invention, hydrogen in a hydrogen-rich fuel
stream, such as is obtained, for example, from fuel reforming
processes is purified employing a material specifically tailored
for and embedded in a purification device for the separation and
purification of hydrogen.
The material employed in the method of this invention comprises at
least one polyoxometalate (POM), a combination of a polymer, metal
oxide and ligand, which is capable of selectively removing the
impurities of interest. For purification of hydrogen from a
hydrogen-rich stream, the impurities typically include HCl,
CO.sub.2, H.sub.2S and/or NH.sub.3. In accordance with one
preferred embodiment of this invention, the POM is disposed within
a porous material. This material can remove polar molecules, such
as H.sub.2S, HCl, NH.sub.3 and water as well as other impurities,
such as CO and CO.sub.2. This material and the method of its use,
in addition to removing impurities from the hydrogen gas streams
which are generated from natural gas reformers or coal gasification
hydrogen generators and removing impurities during gaseous stream
processing, such as natural gas processing, also reduce the size of
the equipment used for pressure swing absorption (PSA). When used,
for example, in connection with hydrogen gas streams, with smaller
PSA equipment, the loss of hydrogen between adsorption and
regeneration swings also becomes much smaller. Thus, overall
efficiency is increased and the PSA equipment size, cost and
operating costs are reduced with effective impurity removal.
Selective separation of impurities from a gaseous stream comprising
the impurities to produce a cleaner gaseous stream is accomplished
in accordance with one embodiment of this invention by contacting a
porous material comprising at least one polyoxometalate material
with the gaseous stream and passing at least a portion of one of
the impurities in the gaseous stream through the porous material,
producing at least a partially purified gaseous stream.
In accordance with one embodiment of this invention, the gaseous
stream is a hydrogen-rich stream comprising H.sub.2S, HCl, and
NH.sub.3 and selective removal of these impurities therein produces
substantially purified hydrogen. Exemplary of a POM-based material
suitable for use in this embodiment of the method of this invention
is [Cu.sub.2(4,4'-bpy).sub.2{Mo.sub.2O.sub.7}].sub.n, (where bpy is
bipyridine), which is a polymer having CuO functions for the
adsorption of H.sub.2S, a pyridine ring to adsorb HCl, and Cu or Mo
to adsorb NH.sub.3. These adsorptions have weak adsorption forces
between the gases and the adsorption sites due to the ligand effect
and site resistance. Therefore, these reversible adsorption
materials adsorb impurities on one side and desorb the impurities
on the other side of a separation wall comprising the POM-based
material.
The entire method of this invention may be continuous. The purity
of the final gas depends upon the length of the gas travel path,
that is, the gas retention time in the device. The POM-based
material may be embedded in a porous ceramic material and in
accordance with one preferred embodiment of this invention is
embedded in an Al.sub.sO.sub.3-based ceramic tube. The ceramic tube
removes water and the POM-based material disposed in the ceramic
tube prevents hydrogen permeate and removes impurities.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of this invention will be
better understood from the following detailed description taken in
conjunction with the drawings wherein:
FIG. 1 is a diagram showing a conventional PSA reformate hydrogen
purification process;
FIG. 2 is a diagram showing a PSA reformate hydrogen purification
process with a POM-based purifier in accordance with one embodiment
of this invention;
FIG. 3 is a schematic diagram of a hydrogen purification device in
accordance with one embodiment of this invention;
FIG. 4 is a schematic diagram of an experimental set-up employed
for the purpose of determining the H.sub.2S removal capabilities of
a POM-based material in accordance with one embodiment of this
invention;
FIG. 5 is a diagram showing typical gas chromatographic signals
from the sweep gas employed in accordance with one embodiment of
the method of this invention; and
FIG. 6 is a diagram showing H.sub.2S concentration in the sweep gas
as a function of temperature.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
This invention involves the use of polyoxometalates for separation
of contaminants or impurities from, and purification of, gaseous
streams comprising one or more such contaminants or impurities. The
invention is suitable for use on gaseous streams at high
temperatures, i.e. in the range of about 200.degree. C. to about
400.degree. C., as well as at lower temperatures. Although suitable
for separation of contaminants or impurities from a variety of
gaseous streams including flue gases and reformates, the method of
this invention is particularly attractive for purification of
hydrogen in by-product streams from natural gas, coal gasification
and/or fossil fuel reforming processes. In addition to hydrogen,
these by-product streams typically comprise H.sub.2S, CO.sub.2, CO,
HCl, NH.sub.3 and water, one or more of which can be detrimental to
the successful operation of hydrogen-based applications, such as
distributed polymer electrolyte membrane fuel cell power systems
and hydrogen vehicle refueling stations.
The polyoxometalate-based organic-inorganic hybrid materials
employed in the method of this invention have the attributes of the
conventional low temperature membrane separation and high
temperature CuO/ZnO catalyst adsorbent for gas purification. The
polyoxometalate-based materials employable in accordance with one
embodiment of the method of this invention comprise
nitrogen-containing ligands. In accordance with preferred
embodiments of this invention, the nitrogen-containing ligand is
selected from the group consisting of amines, pyrroles, pyridines,
imidazoles, and combinations thereof. In addition, the
polyoxometalate-based materials in accordance with one embodiment
of this invention comprise a metal selected from the group
consisting of Cu, Zn, Mo, Mn, W, and combinations and alloys
thereof. Exemplary of a POM-based material suitable for use in the
method of this invention is
[Cu.sub.2(4,4'-bpy).sub.2{Mo.sub.2O.sub.7}].sub.n, the structure of
which is
##STR00001## As previously indicated, the CuO functions to adsorb
H.sub.2S, the pyridine ring functions to adsorb HCl, and the Cu or
Mo function to adsorb NH.sub.3.
Another POM-based material suitable for use in the method of this
invention is similar to the above polymer, but with
poly(4-vinylpyridine) and has the following structure:
##STR00002##
Yet another POM-based material suitable for use in accordance with
one embodiment of this invention is poly(2,5-benzimidazole)
(ABPBI), which has the following structure:
##STR00003##
FIGS. 1 and 2 show complete fuel processing-purification systems to
produce hydrogen from reformate fuel produced by steam-methane
reforming. In the conventional system shown in FIG. 1, purified
hydrogen for either a refueling station or for distributed
generation polymer electrolyte membrane fuel cells is produced. As
shown, the reformate gases from the fuel processor are dried to
remove excess water prior to compression to about 4 to 6
atmospheres pressure for the PSA operation. In this case, the PSA
equipment size is quite large because its design is dominated by
the high concentration of CO.sub.2, trace H.sub.2S, HCl, and
NH.sub.3 in the gases going through compression and into the PSA
process. In contrast thereto, in the system of FIG. 2 employing the
POM-based materials in accordance with the method of this
invention, the PSA equipment size is substantially smaller, with
less hydrogen losses, lower equipment costs and reduced horsepower
requirements due to the knock-out of water and removal of
impurities prior to compression of the gases entering the PSA
process. In this case, both the impurities and the PSA sweep gas
are directed back to the fuel processor burner zone for
environmental control.
The application of the POM-based material to remove H.sub.2S from
H.sub.2S-containing gaseous streams in accordance with one
embodiment of this invention eliminates the conventionally employed
zinc oxide desulfurizer system. Other suitable applications for
POM-based materials in accordance with this invention include acid
gas removal from subquality natural gas and treatment of
biomass-related gases. Successful implementation of this low-cost
POM-based material for separation of CO.sub.2 from H.sub.2 in
reformate streams produced from natural gas steam reforming reduces
the cost and complexity of present gas cleanup technology. Yet
another suitable application of the POM-based material is in
connection with sensors for detecting the presence and/or
concentration of contaminants in a gaseous stream, as well as
enhancing the sensitivity of gas sensors by removing components of
a gaseous stream which may interfere with the detection
capabilities of the sensor.
FIG. 3 shows an apparatus for carrying out the method of this
invention comprising a porous ceramic tube 20 having a gas inlet
end 21 and a gas outlet end 22. A POM-based material is embedded
within the porous wall of the porous ceramic tube. Embedding of the
POM-based material may be achieved dip-coating and/or penetration
into the pores of the ceramic tube. In operation, the hydrogen-rich
gas is passed through the gas inlet end 21 and the interior of the
ceramic tube, water and impurities in the hydrogen-rich gas are
removed through the porous tube walls by means of vacuum extraction
or sweep gas purge, and clean hydrogen gas with a reduced amount of
water is removed from the gas outlet end 22 of the tube.
EXAMPLE 1
In this example, the synthesis of a POM-based material suitable for
use in accordance with one embodiment of the method of this
invention was carried out by the hydrothermal reaction of the
following ingredients in the molar ratio of 1:1:1:0.5:500: Sodium
molybdate dihydride: 2.42 g (Aldrich Chemicals) Copper (II) sulfate
penta hydrite: 2.50 g (Aldrich Chemicals) 4,4'-Bipyridyl: 1.56 g
(Aldrich Chemicals) Arsenic (III) Oxide: 0.98 g Aldrich Chemicals)
Deionized water: 90.0 g The above materials were charged into a
TEFLON.RTM. beaker and then put into a stainless steel bomb fitted
with a stirrer. The stainless steel bomb was wrapped with heating
tape and heated to about 170.degree. C. The reaction was carried
out for 5 days with slow stirring. The bomb pressure during the
reaction time rose to 100-150 psi. After 5 days of reaction time,
the stainless steel bomb was cooled down, depressurized and opened.
Greenish powder settled down at the bottom was filtered and washed
four times with deionized water and then dried in oven at
100.degree. C.
EXAMPLE 2
In this example, the synthesis of a POM-based material suitable for
use in accordance with one embodiment of the method of this
invention was carried out as in Example 1 with the exception that
4,4'-bipyridyl was replaced with poly(4-vinylpyridine).
EXAMPLE 3
In this example, the POM-based material was formed into membranes
by compression molding at 500.degree. F. and 34,000 psi of the
powder produced in Examples 1 and 2 into circular disk of 1.25''
and about 3.5-mil thickness. The molded disk resulting from the
compression of the powder of Example 2 is relatively stronger than
the molded disk produced from the compression of the powder of
Example 1 and, thus, is preferred.
EXAMPLE 4
In this example, a binder material,
poly(oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene)
(PEEK, Victrex USA Inc), was added to the POM-based powder to
improve the strength of the membrane. PEEK is a high temperature
plastic requiring temperatures of about 400.degree. C. to melt.
EXAMPLE 5
In this example, polysulfone (Udel, Solvay Advanced Polymer) was
added as a binder to the POM-based powder to improve the strength
of the membrane. The resulting membrane was both strong and
tough.
EXAMPLE 6
In this example, a POM-based membrane was produced by dispersing a
very fine POM-based powder in a solution comprising
polyethylenamine (PEI), PEVOH, a copolymer of ethylene and vinyl
alcohol, and dimethyl sulfoxide (DMS) in the following
proportions:
TABLE-US-00001 PEVOH (10% solution in DMS) 40.0 g (Aldrich
Chemicals) PEI (10% solution in DMS) 10.0 g (Aldrich Chemicals)
POM-based powder 2.0 g (Lab synthesized) Formaldehyde (38%
solution) 1.0 g (Aldrich Chemicals)
After thorough mixing of all of these ingredients, the membrane was
cast on a polytetrafluoroethylene (PTFE) substrate using glass rod
and dried over night. The dry membrane was then immersed in
deionized water for half hour to leach out the remaining solvent.
The wet membrane was wiped with tissue and then heated in an oven
at 100.degree. C. for about one (1) hour.
EXAMPLE 7
In this example, to increase the elevated temperature stability of
the POM-based membrane, the POM-based material was dispersed in a
high temperature poly(2,5-Benzimidazole), ABPBI polymer solution in
the following proportions and then cast to form the membrane.
TABLE-US-00002 Poly (2,5-Benzimidazole) ABPBI (2% solution in tri-
25.0 g fluoroacetic acid and phosphoric acid, Acros Chemicals)
PEVOH (10% solution in formic acid, Acros chemical) 2.5 g POM-based
(Lab synthesized, 20% on polymer) very fine 0.1 g powder.
The above ingredients were mixed thoroughly to make a casting dope.
The casting dope was cast onto a PTFE substrate and dried over
night, producing the membrane.
EXAMPLE 8
In this example, a ceramic tube comprising a POM-based material is
prepared by combining Na.sub.2MoO.sub.4.2H.sub.2O,
CuSO.sub.4.5H.sub.2O, poly(4-vinylpyridine) at a molar ratio of
about 1:1:2 (pyridine) and water in a round bottom flask and
heating the mixture to a temperature of about 180.degree. C. for
about two (2) hours. The heated mixture is cooled down after which
it is applied to the porous ceramic tube by a coating technique,
such as dip-coating, known to those skilled in the art. The coated
tube is then heated at about 200.degree. C. for curing.
EXAMPLE 9
In this example, Na.sub.2MoO.sub.4.2H.sub.2O and
CuSO.sub.4.5H.sub.2O at a molar ratio of 1:1 are dissolved in
water. The porous ceramic tube is immersed in the resulting
solution, resulting in saturation of the ceramic tube with
solution. The saturated tube is then immersed in a solution of
poly(4-vinylpyridine) for about 30 minutes after which it is
removed from the solution and cured at about 200.degree. C.
EXAMPLE 10
In this example, Na.sub.2MoO.sub.4.2H.sub.2O, CuSO.sub.4.5H.sub.2O,
(4,4'-bipyridine), and As.sub.2O.sub.3, at a molar ratio of about
1:1:1:0.5, are dissolved in water. The Cu.sup.2+ and
MoO.sub.4.sup.2- concentration are about 2 M. The porous ceramic
tube is saturated with the resulting solution after which the
saturated tube is cured at about 180.degree. C. for about 2
hours.
Using the experimental setup shown in FIG. 4, a sample gas
comprising 99% by volume nitrogen and 1% by volume hydrogen sulfide
was introduced at a sample gas flow rate of about 48.3 l/min into
the sample gas side 31 of a cell 30 having a sample gas side and a
sweep gas side 32 and a sweep gas comprising 100% methane was
introduced at a sweep gas flow rate of about 5.5 l/min into the
sweep gas side of the cell, which sweep gas side was separated from
the sample gas side by a POM-based membrane having a thickness of
about 2 mils. The sweep gas was used to carry hydrogen sulfide
diffusing through the POM-based membrane away from the cell.
Gas chromatographic analysis of the H.sub.2S-laden methane sweep
gas produced the GC signals shown in FIG. 5. As shown, although the
hydrogen sulfide content of the sample gas flowing through the
sample gas side of the cell was only about 1%, the hydrogen sulfide
concentration in the sweep gas was about 22% by volume. Although
not intending to be bound by any single explanation for this
surprising result, in spite of the relatively low sweep gas flow
rate, it is believed that the amount of hydrogen sulfide in the
sweep gas is a function of the velocity of the sweep gas at the
surface of the POM-based membrane.
FIG. 6 shows the effect of temperature on the concentration of
hydrogen sulfide in the sweep gas. As shown therein, as the
temperature of the POM-based membrane increases, the diffusivity of
the hydrogen sulfide in the sample gas decreases.
While in the foregoing specification this invention has been
described in relation to certain preferred embodiments thereof, and
many details have been set forth for the purpose of illustration,
it will be apparent to those skilled in the art that the invention
is susceptible to additional embodiments and that certain of the
details described herein can be varied considerably without
departing from the basic principles of this invention.
* * * * *